Supersonic flight over the United States and other countries is a challenging environmental issue for a viable supersonic commercial aircraft. Current FAA regulations prohibit civil flights at Mach numbers greater than one without case-by-case exceptions approved by the Administrator. Many other countries have similar restrictions.
Previous research has shown that the highly impulsive nature of the xe2x80x9cN-wavexe2x80x9d sonic-boom signatures of all existing supersonic aircraft is the primary cause of negative response and regulatory limitations on supersonic travel. Conclusions of NASA research further indicate the exceptional difficulty of designing an aircraft with an xe2x80x9cN-wavexe2x80x9d signature of sufficiently low amplitude for general public acceptance. However, the research also found that a xe2x80x9cshapedxe2x80x9d signature was less objectionable and that a reasonably achievable amplitude wave could meet Committee on Hearing and Bioacoustics of the National Research Council (CHABA) guideline for acceptable noise impact to the general public, depending on frequency of exposure.
A sonic boom occurs due to pressure waves that occur when an aircraft moves at supersonic speeds. During subsonic flight, air displaced by a passing plane flows around the plane in the manner water flows around an object in a stream. However, for a plane flying at supersonic speeds, the air cannot easily flow around the plane and is instead compressed, generating a pressure pulse through the atmosphere. The pressure pulse intensity decreases as a consequence of movement from the airplane, and changes shape into an N-shaped wave within which pressure raises sharply, gradually declines, then rapidly returns to ambient atmospheric pressure. A wall of compressed air that moves at airplane speed spreads from the wave and, in passing over ground, is heard and felt as a sonic boom. The rapid changes in pressure at the beginning and end of the N-wave produce the signature double bang of the sonic boom.
Research has recently shown that boom intensity can be reduced by altering aircraft shape, size, and weight. For example, small airplanes create a smaller amplitude boom due to a lower amount of air displacement. Similarly, a lighter aircraft produces a smaller boom since an airplane rests on a column of compressed air and a lighter plane generates a lower pressure column. An aircraft that is long in proportion to weight spreads the N-wave across a greater distance, resulting in a lower peak pressure. Furthermore, wings that are spread along the body and not concentrated in the center as in a conventional aircraft produces a pressure pulse that is similarly spread, resulting in a smaller sonic boom.
Shaping of a sonic boom refers to a technique of altering source pressure disturbance such that a non-N-wave shape is imposed on the ground. Shaping sonic boom can reduce loudness by 15-20 dB or higher with no added energy beyond that to sustain flight. Shaping to minimize loudness is based on insight regarding changes in aircraft pressure disturbances during propagation to the ground.
Shaped sonic booms are only achieved deliberately. No existing aircraft creates a shaped sonic boom that persists for more than a fraction of the distance to the ground while flying at an efficient cruise altitude since non-shaped pressure distributions quickly coalesce into the fundamental N-wave shape. The N-wave form generates the largest possible shock magnitude from a particular disturbance. The N-wave shape results because the front of a supersonic aircraft generates an increase in ambient pressure while the rear generates a decrease in pressure. Variation in propagation speed stretches the disturbance during propagation to the ground. Shaped boom techniques typically attempt to prevent coalescing of the pressure disturbance by adding a large compression at the aircraft nose and an expansion at the tail with pressure in between constrained between the compression and expansion. The shaped boom stretches the ends of the signature faster than the in-between pressures, creating a non-N-wave sonic boom at the ground.
Boom reduction makes a supersonic aircraft less objectionable by minimizing the loudness of a sonic boom. Audible frequencies in a sonic boom occur in the rapid pressure changes, or shocks, at the beginning and end of the typical N-waveform. More quiet shocks have decreased pressure amplitudes and increased pressure change time durations.
Although sonic boom reduction is an important design criterion for a supersonic aircraft, other considerations always impact design decisions. For example, a useful aircraft will have an appropriate capacity for holding passengers and/or cargo and be a suitable configuration for safe operation. Some design aspects include integration of landing gear and airframe.
What is desired is a supersonic aircraft with tail and control structures that effectively control the aircraft in subsonic, transonic, and supersonic flight, and enable sonic boom reduction or minimization.
In accordance with some embodiments of the disclosed aeronautical system, a supersonic aircraft comprises a wing having upper and lower surfaces and extending from a leading edge to a trailing edge and at least two engine nacelles coupled to the lower surface of the wing on the trailing edge. The supersonic aircraft further comprises an inverted V-tail coupled to the wing comprising a central vertical stabilizer, at least two inverted stabilizers coupled to sides of the central vertical stabilizer and coupled to the wing and supporting at least two engine nacelles, and at least two ruddervators respectively pivotally coupled to at least two inverted stabilizers. The supersonic aircraft also comprises a controller coupled to at least two ruddervators and capable of adjusting the aircraft longitudinal lift distribution throughout a flight envelope to maintain a reduced sonic boom and reduced drag trim condition.
According to other embodiments, a supersonic aircraft comprises a wing having upper and lower surfaces and extending forward from a leading edge aft to a trailing edge, and an inverted V-tail coupled to the wing comprising a central vertical stabilizer with leading and trailing edges, and at least two inverted stabilizers coupled to sides of the central vertical stabilizer and coupled to the wing. The aircraft further comprises a rudder pivotally mounted on the trailing edge of the central vertical stabilizer. The rudder has a sufficient area and rudder control sizing to enable adequate yaw acceleration to achieve at least 8 degrees of yaw angle change within four seconds for decrab and a rudder actuator rate less than 60 degrees/second.
In accordance with other embodiments, a supersonic aircraft comprises a fuselage extending forward and aft about a longitudinal axis. The fuselage has upper and lower surfaces. The lower surface has a general axial curvature about the longitudinal axis and a local aft flattening. The aft flattening of the fuselage adds lateral stiffening to the aircraft structure. The aircraft further comprises a wing coupled inboard to the fuselage and extending outboard, and having a forward leading edge to an aft trailing edge. The aircraft also comprises an inverted V-tail coupled to the wing and fuselage comprising a central vertical stabilizer, at least two inverted stabilizers coupled to sides of the central vertical stabilizer and to the wing outboard of the fuselage. Furthermore, the aircraft comprises a strake coupled to and extending from the central vertical stabilizer through the fuselage interior and coupling to the lower fuselage surface at the position of local aft flattening.
According to further additional embodiments, a supersonic aircraft comprises a wing having upper and lower surfaces and extending from a leading edge to a trailing edge, at least two engine nacelles coupled to the lower surface of the wing on the trailing edge, and an inverted V-tail coupled to the wing. The inverted V-tail comprises a central vertical stabilizer, at least two inverted stabilizers coupled to sides of the central vertical stabilizer and coupled to the wing and supporting at least two engine nacelles. The aircraft further comprises at least two wing structural support members coupled to the upper surface of the wing generally overlying at least two engine nacelles. The wing structural support members couple between the inverted stabilizers and the wing and extend from the wing trailing edge forward. The structural support members add support to assist carrying engine nacelles weight.